1. Field of the Invention
The invention relates to an ink ejecting device having an ink ejecting head which is installed exchangeably therein.
2. Description of Related Art
In a conventional ink ejecting device, the ink ejecting head can be easily detached from the ink ejecting device and exchanged with a new one in consideration of the durability of the driving elements in the ink ejecting head. This type of ink ejecting device can be used much longer if the ink ejecting head is exchanged with a new one. Therefore, this type of device is very useful to users. There is a proposal that the head exchange time for such a device is determined for the user by counting the number of driving times of the driving element of the head and, at a predetermined count, replacing the ink ejecting head to prevent a decrease in the printing quality.
On the other hand, U.S. Pat. No. 5,202,702 discloses ink ejecting devices having a cleaning mechanism for cleaning the ink ejecting head. A wiper slides on a nozzle surface to clean dust or ink drip from the nozzle surface. Further, a water-repellent layer formed on the nozzle surface prevents unnecessary ink droplets from sticking to the nozzle surface. Due to the wiper and the water-repellent layer, ink droplets are ejected straight and exactly toward a printing medium. Recent ink ejecting devices have both the above-mentioned wiper and the water-repellent layer to achieve a higher-level printing quality. In these types of devices, the nozzle surface is cleaned by the wiper when the power is turned on or off, during printing operations, or after a predetermined number of characters or a predetermined number of pages have been printed.
However, since the driving elements of the ink ejecting devices have a longer durability, the exchange time is not determined until the driving elements are driven for quite a long time.
On the other hand, in the ink ejecting devices having both the wiper and the water-repellent layer, the water-repellent layer on the nozzle surface flakes off gradually whenever the cleaning operation is performed. Therefore, since it cannot be prevented that unnecessary ink droplets stick to the nozzle surface as the water-repellent layer is degraded, the printing quality is decreased. Especially if a pigment ink having good printing quality is used and the nozzle surface is cleaned sandwiching particles of the pigment ink between the water-repellent layer and the wiper, there is possibility that the water-repellent layer is easily flaked off. Moreover, since the cleaning operation is made whenever the power is turned on or off, the water-repellent layer flakes off more rapidly if the power is frequently turned on or off.
Since, in such ink ejecting devices, the cleaning operation occurs with the same timing as before the flaking-off of the water-repellent layer even after the water-repellent layer flakes off, unnecessary ink droplets stick to the nozzle surface for a long period of time and the printing quality is decreased during that period. It is possible that the user recognizes or the device has means to recognize the decrease in the printing quality for replacement of the ink ejecting head to thereby solve the above-mentioned problem. However, an ink ejecting head for use as a replacement is not always prepared for the user. In this case, the ink ejecting device cannot be used until the user obtains an ink ejecting head for replacement.
When the above-mentioned head exchange informing function is applied to the ink ejecting device having both the wiper and the water-repellent layer, the water-repellent layer flakes off before the driving elements wear out. Therefore, the printing quality decreases and the user normally does not notice the decrease in the printing quality, at least not until it has significantly decreased.